The present invention relates generally to radiographic imaging devices, particularly, computed tomography (CT) imaging devices, and the like, and more specifically, to apparatus and methods for separating noise caused by X-ray scatter contaminations from the primary signal of the detector of a radiographic imaging device so that the scatter may be reduced or eliminated from the signal, thereby allowing the image quality of the radiographic imaging device to be improved.
Single-row CT imaging devices or scanners, as well as CT imaging devices employing quasi-linear multi-row detectors, typically employ thin, straight metal collimators for eliminating scatter radiation. These metal collimators are oriented such that most of the scattered rays, which have their source at the scatter centers in the object being imaged (e.g., the body of a patient), intersect the collimator at oblique angles and are blocked. As a result, only rays approaching the detector directly from the direction of the radiation source pass through the collimator to the detector.
Cone-beam computed tomography (CBCT) imaging devices employ two-dimensional area detectors (typically referred to in the art as flat panels) in all cone beam imaging applications, be it conventional X-ray imaging or cone-beam computed tomography. CBCT imaging devices have typically been used for the reconstruction of high-contrast objects, such as bone or contrast filled vasculature. When used in such applications it is not necessary for the CBCT device to compensate for scatter radiation, since scatter induced noise is below the signal of interest. However, when used for soft tissue resolution, it becomes necessary to eliminate noise caused by scatter radiation to provide desired image quality.
To effectively block scatter radiation from the area detectors used by CBCT imaging devices using conventional technology, conically shaped collimators may be provided for each detection element of the area detector. Such collimators would be physically impractical to manufacture and maintain, especially in CBCT imaging devices employing megavolt (MV) sources, where the collimators would require substantial mass in order to block the high-energy photons created by the X-ray source. As a result, conventional metal collimators such as those used in single-row CT imaging devices are impractical to be used to block scatter radiation from the area detectors for CBCT imaging devices.
Consequently, it would be desirable to provide a method for separating the noise caused by X-ray scatter contaminations from the primary signal component of the signal produced by the detector of a radiographic imaging device so that the scatter induced noise in the signal may be reduced or eliminated without the use of metal collimators or like shielding devices.